The invention relates to a method for correcting defective solder-bump-arrays and an apparatus for performing said method.
Solder bumps are electrically conducting contact elements and are used, for example, for the production of semiconductor elements according to the flip-chip-technology, in which the chip or die is provided on its active contacting side with solder bumps and subsequently connected to the active side of the substrate (circuit plate, carrier) via said solder bumps, i.e., without any connection cables. Advantages of this technology are the particularly small dimensions of the package yielded in this manner, the smaller dimensions of the connections, and the short connection lengths. This way high connection density, low production costs, and high functionality of the package can be achieved.
Various methods are known to produce solder bumps.
According to a first method the wafer is first coated over its entire surface with metal and subsequently a lacquer reticle is applied, which is provided with openings above the contact sites of the chips. Subsequently, a metal alloy (the solder) is released galvanically and first the lacquer reticle and then the areas of the metal layer not coated by the released solder are removed by selective etching. Then the solder cylinders are melted to small solder bumps (reflow). In the following, the chips or dies are separated by cutting the wafers. The chips are then moistened with a flux material and placed with their active contacting side onto the active side of the substrate. By heating the entire structure the solder bumps are melted and thus an electric connection is created between the contact surfaces of the chips and the contacts of the substrate (reflow soldering).
The solder bumps may also be prefabricated outside the wafer, for example, and subsequently applied to the wafer. For this purpose, a matrix made from glass (mold) is used having a grid in the X-direction and in the Y-direction, on which the solder bumps are arranged for all chips located on a wafer, for example in a so-called solder-bump-array. The mold provides the array-structure to be produced in the form of cavities accepting the solder-bumps. In order to produce the solder bumps these cavities are filled with molten solder using a doctor. After the solder has set the solder bumps are provided in the required arrangement for the entire wafer. In a later process, this arrangement of solder bumps is transferred from the mold onto the chips or dies still located in the wafer-laminate.
It has shown that in this method various defects can occur. For example, it can happen that individual cavities are insufficiently filled with solder or not at all. Other potential defects comprise that individual cavities are filled with too much solder or that neighboring cavities are connected to each other by bridges of soldering material.
In order to ensure the functionality of the dies produced from wafers it is necessary to identify and correct such defects before the solder-bump-array is transferred onto the wafer. Therefore the object of the present invention is to provide a method and a device to correct defective solder-bump-arrays.